1. Field of the Invention
The present invention relates to the delivery of emulsion explosives compositions, including non-sensitised emulsions for explosives' use. In particular, the present invention relates to an apparatus and process for charging a blasthole with an emulsion explosives composition and/or, for example, for transferring emulsion explosives composition from one container to another.
2. Description of the Related Art
The delivery of many types of explosives is typically conducted by the use of pumps such as piston pumps and progressive cavity pumps because of the relatively high pressures usually required. However, the passage of emulsion explosives compositions through these pumps, even in non-sensitised condition, is potentially hazardous as failures in the pumping mechanisms can lead to excessive heat or pressure being applied to the material and can cause accidental explosion.
It has been proposed to alleviate these disadvantages in some circumstances by delivering emulsion explosives compositions pneumatically. Pneumatic loading of one of the most common forms of commercial explosives, ammonium nitrate/fuel oil mixtures (ANFO), is well known. ANFO is a dry explosive with good flow qualities and delivery into a borehole is commonly performed through a valved outlet in the bottom of a pressure vessel containing the ANFO at a pressure in the range of 200-600 KPa.
As described in International Patent Application WO 98/10237, adopting a similar proposal for emulsion explosives compositions can remove control in the amount of material loaded into the borehole and produce undesirable splash and waste at the required pressures. In WO 98/10237 these disadvantages are proposed to be alleviated by adopting an incompressible liquid such as water to pressurise a substantial volume of the emulsion explosives composition in a pressure kettle.
The use of water for charging blastholes with emulsion explosives compositions is undesirable because the water can be absorbed into the emulsion, with even small absorbed amounts reducing the blasting energy of the emulsion, increasing the critical diameter and reducing the sensitivity of the emulsion. Additionally, large volumes of potentially contaminated water must then be disposed of.
The pneumatic charging of emulsion explosives compositions is also described in British Patent Application GB 2204343. In this proposal, a non-explosive base emulsion and a gassing solution are transferred into a loading hose from respective hoppers by means of compressed air. They are mixed in a homogeniser at an outlet end of a lance connected to the hose. Prior to being mixed together the gassing solution surrounds the base emulsion in the hose to lubricate the passage of the base emulsion therethrough and allow lower pressures to be used in the hoppers. The supply of compressed air to the hoppers, and therefore the delivery of emulsion explosive from the lance, is controlled by a shut-off value on the lance which is biased into its closed condition. Thus an operator adjacent to the blasthole collar must manually hold the shut-off valve open.
It is suggested in GB 2204343 that it is preferred to use respective pumps for feeding the base emulsion and gassing solution into the loading hose, in place of compressed air in the hoppers.
International patent application WO 97/48966 also proposes the pneumatic delivery of emulsion explosives compositions to boreholes. The arrangement described is similar to that in GB 2204343 except that lubrication of the material being delivered is provided by an annular stream of water around the material in the delivery hose. Additional ways of maintaining relatively low extrusion pressures are described, including keeping the internal diameter of the delivery hose and associated components as large as possible. Compressed air pressures of about 240 and 550 KPa are described.
One of the difficulties associated with all of the above proposals for delivering emulsion explosives compositions pneumatically remains the control of the amount of material delivered, given the compressibility of the gas.
The metered delivery of explosives using pneumatic discharge is described in U.S. Pat. No. 5,811,711 which proposes the use of complex metering means, control means and a programmable controller, the metering is then performed by timing the flow or delivery of the explosives.
As described in the aforementioned patent specifications, with conventional pneumatic delivery of emulsion explosives compositions, the whole inventory of the composition available for delivery is pressurised leading to complex apparatus whose use underground is restricted to qualified personnel. The pressurised vessels from which the composition is delivered are also subject to strict controls leading to additional expense both in manufacturing them and in maintaining them.